Hanging a picture perfectly on the wall is a tough task, but its harder when the frame requires two screws or nails. To make this easier, mark the length between the hangers by using strip of tape so you can measure the distance and drill the hols straight.
Just get some painter's tape or masking tape, and stick the tape between the two holes on a frame, and that would give you a good gauge on the distance of the holes. Then, take the tape and stick it on your wall and check to make sure its straight up leveled. Then you start drilling the holes.